Segredos numa semente: pistas sobre a evolução das primeiras flores

quarta-feira, outubro 28, 2009

Secrets In A Seed: Clues Into The Evolution Of The First Flowers

ScienceDaily (Oct. 28, 2009) — Approximately 120-130 million years ago, one of the most significant events in the history of the Earth occurred: the first flowering plants, or angiosperms, arose. In the late 1800s, Darwin referred to their development as an "abominable mystery." To this day, scientists are still challenged by this "mystery" of how angiosperms originated, rapidly diversified, and rose to dominance.

Nymphaea lotus. (Credit: Courtesy of Wikimedia Commons)

Studies of key features of angiosperm evolution, such as the evolution of the flower and development of the endosperm, have contributed to our current understanding of relationships among the early families of flowering plants. Examining the development of seeds and embryos among early angiosperms may help to improve our understanding of how flowering plants evolved from the nonflowering gymnosperms.

A recent study by Dr. Paula Rudall and colleagues explores a piece of this mystery: the microscopic anatomy of seed development in Trithuria, a genus in the plant family Hydatellaceae, thought to be one of the earliest families of angiosperms -- the so-called "basal angiosperms."

Rudall and colleagues' observations of the development of the embryo and endosperm (tissue that surrounds the embryo and provides nutrition) in Trithuria suggest that double fertilization occurs. Double fertilization is a unique feature of flowering plants where one sperm nucleus unites with the egg, producing the embryo, while another sperm nucleus unites with a separate nucleus from the female, producing the endosperm. The endosperm is divided into two regions -- the micropylar and chalazal regions.

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Journal reference:

Rudall et al. Seed fertilization, development, and germination in Hydatellaceae (Nymphaeales): Implications for endosperm evolution in early angiosperms. American Journal of Botany, 2009; 96 (9): 1581 DOI: 10.3732/ajb.0900033

Adapted from materials provided by American Journal of Botany, via EurekAlert!, a service of AAAS.